Construction and arrangement of wipers in thin-film evaporators



y 1, 1963 o. PINKWART ETAL 3,090,732

CONSTRUCTION AND ARRANGEMENT OF WIPERS IN THIN-FILM EVAPORATORS Filed May 5, 1959 2 Sheets-Sheet 1 &

ATTORNEY y 21, 1953 D. PINKWART ETAL 3,090,732

CONSTRUCTION AND ARRANGEMENT OF WIPERS IN THIN-FILM EVAPORATORS Filed May 5, 1959 2 Sheets-Sheet 2 INVENTORS.

RUDOLF SC HNE/DER. EMIL GRUBEP. WERNER STR/TTMATTEIL ATTORNEY United States Patent Olitice 3,090,732 Patented May 21, 1963 3,090,732 CONSTRUCTION AND ARRANGEMENT OF WIPEKQ IN THIN-FILM EVAPORATORS Dieter Pinkwart, Cologne-Mulheim, Rudolf Schneider,

Krefeld-Uerdingen, and Werner Strittmatter, Butzbach,

Hesse, Germany, and Emil Gruber, Zurich, Switzerland, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany Filed May 5, 1959, Ser. No. 811,099 Claims priority, application Germany May 7, 1958 15 Claims. (Cl. 202-236) The invention relates to the construction and arrangement of wipers in thin-film evaporators, in which the blade-shaped wipers for spreading the liquid to be treated over a heated wall are arranged on a stirrer mechanism.

The danger exists with the evaporators of this known type that during the evaporation, parts of the film are detached from the wall and are entrained as foam, drops or mist by the vapour stream passing to the condenser. Although the use of the conventional wipers produces a considerable improvement in the film and separation conditions by comparison with the simple free-drop evaporator, it is diflicult to prevent completely the splashing of drops, and these dilute the residue to be concen trated or contaminate the distillate.

The danger of such unevaporated liquid being carried to the condenser is most marked when the condenser is arranged inside the evaporator opposite the evaporation surfaces. With this type of construction, however, there is also a considerable reduction in the efficiency of the condenser if heat radiation from the evaporation surfaces can reach the condensation surfaces. Similarly, the capacity of the evaporator surface is reduced by heat radiation, and the required heat input becomes disadvantageously high.

It has now been found that the separation into drops of the liquid to be evaporated is minimized and, with an evaporator having a built-in condenser, at the same time a suppression of the heat radiation between evaporation and condensation surfaces is obtained if, in accordance with the invention, the wipers of the stirrer mechanism overlap louvre fashion, but still at a distance from one another. With an evaporator having a built-in condenser, those edges of the stirrer vanes which face the evaporation surface extend rearwardiy in relation to those edges facing the condensation surface, when seen in the direction of rotation, and the vanes overlap in louvre formation or in form of reales with such a spacing that it is not possible from any position on the condenser surface to see any point of the evaporator surface. The stirrer vanes can be constructed as wipers pivotally a1- rangcd about pins or as stirrer vanes secured fast to the stirrer mechanism and they can be given an arcuate curvature, so as to aerodynamically improve the rotation of the vapour column ascending inside the evaporator vessel. The blade-shaped stirrer vanes are preferably formed with radial incision at their longitudinal sides; the lugs between the incisions are bent out of the plane of the vane. The lugs or flaps form separate helical elements for spreading the liquid, the edges of these eicrnents sweeping past close to the inside wall of the evaporator or rubbing thereon if the wipers are pivotally arranged. Each vane has a relatively large number of such flaps, all of which are bent out in the same direction from the plane of the vane. In order to shorten or lengthen the residence time of the liquid in the evaporator, the flaps of a stirrer vane or alternately the adjacent stirrer vanes can be set at such an inclination that they wipe the liquid downwardly or upwardly. If a long residence time is desired, all fiaps are set with an upward inclination, so that they have a conveying effect opposite to the liquid running down because of gravity. Por shortening the residence time, all flaps are set with a downward inclination.

A wide range of combinations are possible in which some flaps wipe upwardly and some downwardly.

It is true that evaporators having fittings in louvre formation are known, but these fittings serve as condenser surfaces and have no wiper action. Louvre-type fittings are also known which serve as spray separators. These fittings also have no wiper action and give no complete protection against radiation. The vanes arranged in louvre formation closely adjacent one another on the stirrer mechanism, as provided according to the invention, simplify the construction of an evaporator with a built-in condenser; space is saved, whereby the distance between the evaporation surface and condensate surface can be kept smaller, this being particularly advantageous in connection with high vacuum distillation and molecular distillation. Due to the more compact assembly and the lack of need to supply particular protection against radiation, the method of construction is more economical.

Embodiments of the invention are shown diagrammatically and by way of example in the drawing. In the drawing,

FIGURE 1 is a longitudinal section through the evaporator with a condenser arranged outside the evaporator.

FIGURES 2, 3 and 4 represent ci'osssections through wiper-type stirrers the pivoted wiper blades of which are of different shapes.

FIGURE 5 is a longitudinal section through the evaporator with a built-in condenser and having pivotally arranged stirrer vanes acting as wipers, and

FIGURE 6 is a cross-section through this evaporator on the line a--b.

FIGURES 7 and 8 show cross-sections of an evaporator with rigid stirrer vanes.

FIGURE 9 shows a part of the edge of a stirrer vane, seen in a direction radially towards the axis.

FIGURE 10 illustrates an evaporator cross-section with stirrer vanes constructed as eccentrically mounted angular vanes.

In FIGURE 1:

1 represents the supply line for the liquid to be evaporated,

2 is the liquid distributor,

3 is the evaporator vessel,

4 is the heating jacket of the evaporator vessel,

5 is the outlet for the residue which has not evaporated,

6 is the discharge union for the vapour, which communicates with the vacuum device (not shown).

Wipers 10 pivotally arranged about pins 9 are mounted on the shaft 7 in rings 8 secured concentrically of the shaft, these wipers sweeping over the internal wall of the vessel 3 and thereby distributing the film of liquid running down the Wall. Located at the end of the shaft is a slide surface which is for example constructed as a bearing ring 33 sliding on the internal surface of the vessel and ensuring a centering of the shaft.

As will be seen from FIGURES 2, 3 and 4, the pins 9 of the wipers 10 are so closely arranged louvre-fashion that those edges of the wipers which slide on the cylindrical surface 3 are concealed behind the pivot edge of the following wiper in each case, when seen from the centre of the shaft.

The effect achieved by this arrangement is that drops splashing from the wall are taken up by the following wiper and returned to the wall again by centrifugal force.

FIGURE 3 shows blades with an arcuate curvature, whereby more favourable flow conditions are obtained for the resulting vapour and at the same time the vapour stream rising in the evaporator is caused to rotate. Due to the rotation of the vapour, any entrained drops are again thrown back on to the heated wall.

FIGURE 4 shows another possible arrangement in which the pivot point 9 of each wiper 10 is not at the leading edge of the wiper, but positioned towards the centre of the latter. Such blades ensure the strong rotation of the ascending vapour column.

In FIGURE 5:

11 represent the supply line for the liquid to be evaporated,

12 is the liquid distributor ring,

13 is the evaporator vessel,

14 is the heating jacket of the evaporator vessel,

15 is the outlet for the residue which has not evaporated,

16 is the discharge union for the gases which cannot be condensed, which union communicates with the vacuum device (not shown).

Rings 18, which are connected to reinforcing rods 18a, are fixed concentrically on the shaft 17 and carry the stirrer vanes which are movable about pins 19 and which are in the form of Wipers 20. the latter sweeping over the inside of the vessel 13 and thus distributing the liquid film running down thereon. Located at the end of the shaft is a slide surface in form of a bearing ring 21 which slides on the internal surface of the vessel and ensures centering of the shaft.

As will be seen from FIGURE 6, the wipers are so arranged in louvre formation that those edges of the wipers which slide on the surface of rotation are concealed behind the edge of the following wiper in each case, when seen from the centre 26 of the shaft and also from any point 22:; of the condenser 22 arranged inside the evaporator.

The effect obtained by this arrangement is that drops splashing off the wall are reliably taken up by the follow ing wiper and are returned to the wall again by centrifugal force. Due to the louvre-type overlappipng arrangement of the wipers, direct heat radiation from the heated evaporator surface 13 to the cooled surface of the condenser 22 is prevented and thus not only the thermal efficiency but also simultaneously the capacity of the evaporator is increased and the heat consumption is reduced. In order to avoid heat transfer by reflection at the vanes, these can be provided with a surface layer of low thermal conductivity. Numeral 26 represents the supply pipe for the coolant, while 23 is the discharge pipe; the condensate running down along the condenser 22 is discharged through the pipe 24 provided with a collecting conduit 24a.

FIGURES 7, 8 and 9 illustrate cross-sections through an evaporator, the vanes 27 of which are secured fast to the rings 18 of the stirrer mechanism.

The vanes 20 or 27 are formed at their outer edges with flaps or lugs 28 (FIG. 8) which are bent out from the plane of the vanes 20 or 27 between the incisions 29 (FIG. 9) in such a way that they form helically curved small blades, the edges of which sweep past the internal wall 13 of the evaporator.

In FIGURE 10, the wiper vanes are in the form of eccentrically mounted pivoted angular vanes 20. The longer wiper arm 31, which sweeps along the evaporator wall, serves for spreading the liquid on the heated wall and as a protection against radiation, while the shorter arm 32 serves as a stripper for the condensation film on the condenser surface 22.

We claim:

1. A thin-film evaporator apparatus comprising a drum means, and a plurality of vane means disposed within said drum means and mounted for rotation therewithin, said drum means having an inner wall evaporator surface adapted for maintaining a thin film of liquid to be evaporated thereon, said vane means being axially disposed in said drum means in sliding abutment with said evaporator surface along a portion of their radially outermost edges and in closely overlapping spaced relation to one another at an angle with respect to the plane of the radius of the drum at any point to form an overlapping vane arrangement annular in cross-section circumferentially closing off direct radial communication between the drum axis and said evaporator surface, whereby with respect to said evaporator surface said vane means are positioned such that any line passing radially from the axis of said drum means to said evaporator surface intersects at least one vane means.

2. A thin-film evaporator apparatus comprising a drum means, a plurality of vane means disposed within said drum means and mounted for rotation therewithin, and a condenser surface means positioned in said drum means axially with respect to said vane means, said drum means having an inner wall evaporator surface adapted for maintaining a thin film of liquid to bc evaporated thereon, said vane means being axially disposed in said drum means in sliding abutment with said evaporator surface along a portion of their radically outermost edges and in closely overlapping spaced relation to one another at an angle with respect to the plane of the radius of the drum at any point to form intermediate said evaporator surface and the condenser surface of said condenser surface means an overlapping vane arrangement annular in crosssection circumferentially closing off direct radial communication between the condenser surface and said evaporator surface, whereby with respect to said evapora tor surface and said condenser surface said vane means are positioned such that any line passing radially from the axis of said drum means through said condenser surface to said evaporator surface intersects at least one vane means.

3. A thin-film evaporator apparatus comprising a drum means, a plurality of vane means disposed Within said drum means and mounted for rotation therewithin, and a condenser surface means positioned in said drum means axially with respect to said vane means, said drum means having an inner wall evaporator surface adapted for main taining a thin-film of liquid to be evaporated therein, said vane means being disposed in said drum means in overlapping spaced relation to one another and mounted for rotation intermediate said evaporator surface and the condenser surface of said condenser surface means such that with respect to said evaporator surface and said condenser surface any line passing from the axis of said drum means through said condenser surface to said evaporator surface intersects at least one vane means, said vane means including a radially outer edge in sliding abutment with said evaporator surface and a radial y inner edge in sliding abutment with said condenser surface.

4. A thin-film evaporator apparatus according to claim 1 wherein said vane means are mounted on a shaft for rotation therewith.

5. A thin-film evaporator apparatus according to claim 4 wherein said shaft is provided with radial extension means for seating said vane means in radially displaced relation with respect to said shaft and in sliding abutment with said evaporator surface.

6. A thin-film evaporator apparatus according to claim 5 wherein said radial extension means are disc means mounted on said shaft and said vane means are seated on said disc means for rotation therewith.

7. A thin-film evaporator apparatus according to claim 1 wherein said vane means are substantially arcuate in shape.

8. A thin-film evaporator apparatus according to claim 1 wherein said vane means are substantially fiat in shape.

9. A thin-film evaporator apparatus according to claim 5 wherein said vane means are fixedly seated on said extension means.

10. A thin-film evaporator apparatus according to to claim 5 wherein said vane means are pivotally seated on said extension means.

11. A thin-film evaporator apparatus according to claim 10 wherein said vane means are arcuate in shape, having a leading and a trailing edge portion, and are pivotally seated at a point intermediate the leading and trailing edge portions.

12. A thimfilm evaporator apparatus according to claim 2 wherein said evaporator is provided with collection means for collecting condensate formed on said condenser surface.

13. A thin-film evaporator apparatus according to claim 12 wherein said vane means are mounted for rotation with a rotatable shaft and are fixedly seated to an annular ring interposed between said evaporator surface and said condenser means to maintain said vane means in overlapping spaced relation.

14, A thin-film evaporator apparatus according to claim 1 wherein said vane means include in their outer edges in sliding abutment with said evaporator surface a plurality of extension flaps diverging from the plane of said van means, the outer edges of said extension flaps slidably abutting said evaporator surface.

15. A thin-film evaporator appartus comprising a drum means, a plurality of vane means disposed within said drum means and mounted for rotation therewithin, and

a condenser surface means positioned in said drum means axially with respect to said vane means, said drum means having an inner wall evaporator surface adapted for maintaining a thin-film of liquid to be evaporated thereon, said vane means being disposed in said drum means in overlapping spaced relation to one another and mounted for rotation intermediate said evaporator surface and the condenser surface of said condenser surface means, such that, with respect to said evaporator surface and said condenser surface, any line passing from the axis of said drum means through said condenser surface to said evaporator surface intersects at least one vane means, said vane means being angularin shape and pivotally mounted intermediate said evaporator surface and said condenser surface with a radially outer edge in sliding abutment with said evaporator surface and radially inner edge in sliding abutment with said condenser surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,403,978 Hickman et al. July 16, 1946 2,500,900 Madlen Mar. 14, 1950 2,546,381 Zahm Mar. 27, 1951 2,766,193 Schneider Oct. 9, 1956 2,848,388 Bueche Aug. 19, 1958 2,974,725 Sanesreuther et al. Mar. 14, 1961 

1. A THIN-FILM EVAPORATOR APPARATUS COMPRISING A DRUM MEANS, AND A PLURALITY OF VANE MEANS DISPOSED WITHIN SAID DRUM MEANS AND MOUNTED FOR ROTATION THEREWITHIN, SAID DRUM MEANS HAVING AN INNER WALL EVAPORATOR SURFACE ADAPTED FOR MAINTAINING A THIN FILM OF LIQUID TO BE EVAPORATED THEREON, SAID VANE MEANS BEING AXIALLY DISPOSED IN SAID DRUM MEANS IN SLIDING ABUTMENT WITH SAID EVAPORATOR SURFACE ALONG A PORTION OF THEIR RADIALLY OUTERMOST EDGES AND IN CLOSELY OVERLAPPING SPACED RELATION TO ONE ANOTHER AT AN ANGLE WITH RESPECT TO THE PLANE OF THE RADIUS OF THE DRUM AT ANY POINT TO FORM AN OVERLAPPING VANE ARRANGEMENT ANNULAR IN CROSS-SECTION CIRCUMFERENTIALLY CLOSING OFF DIRECT RADIAL COMMUNICATION BETWEEN THE DRUM AXIS AND SAID EVAPORATOR SURFACE, WHEREBY WITH RESPECT TO SAID EVAPORATOR SURFACE SAID VANE MEANS ARE POSITIONED SUCH THAT ANY LINE PASSING RADIALLY FROM THE AXIS OF SAID DRUM MEANS TO SAID EVAPORATOR SURFACE INTERSECTS AT LEAST ONE VANE MEANS. 